Radiation has long been used intraoperatively to treat a variety of cancers by delivering a high local dose of radiation directly to the tumor bed through the operative site. Early intraoperative radiation treatment methods utilized x-rays as the radiation source. More recent intraoperative therapy installations have employed beams of high energy electrons as the radiation source to provide a homogeneous dose of radiation with a rapid falloff in radiation intensity beyond the treatment volume, thereby minimizing exposure of noncancerous tissue to the radiation.
In a typical intraoperative electron beam therapy (IOEBT) procedure, the surgeon removes the bulk of the patient's tumor so that minimal residual disease remains. The attending radiation oncologist selects the electron beam energy and field size required to treat the target volume. A single cancerocidal radiation dose is then delivered to the tumor site, while the dose to normal tissues is kept to a minimum. IOEBT has been shown to be especially useful in the treatment of bone sarcomas, soft tissue sarcomas, bronchogenic, gynecological, colorectal, pancreatic and gastric cancers.
The primary drawbacks of present IOEBT systems are size and weight. Equipment currently available to a clinical facility interested in an IOEBT system is a large, 5-10 ton gantry-mounted linear accelerator, operating at 5 to 20 MeV and requiring a specially-designed operating suite with large amounts of radiation shielding and a weight-bearing floor. The weight of the accelerator itself and the need to provide special shielding and structural support for the IOEBT room virtually guarantees that each IOEBT system will be used in only one specialized shielded theater equipped with a dedicated linear accelerator. This dedicated-facility approach requires a large capital outlay on the part of the hospital. More importantly, from a medical point of view, a separate theater makes treatment of the patient much more difficult.
The drawbacks of this situation arise from the need to transport the patient during surgery from the operating room to the radiation oncology room and include increased risk of infection, increased anesthesia requirements, and increased complexity of OR and radiation therapy schedules to accommodate the use of two rooms for a single surgical procedure.
Orthovoltage x-ray treatment equipment is lighter and requires less shielding than IOEBT systems and therefore avoids some of the logistical problems of the IOEBT approach. However, orthovoltage systems have lengthy treatment times, inhomogeneous dose distributions and high bone absorption. These drawbacks limit the clinical efficacy of orthovoltage as an intraoperative treatment procedure.
What has been needed is an IOEBT system that can be used in one or more existing surgical suites without the addition of extensive radiation shielding and structural support to the operating rooms. This invention meets this need by providing a surgical facility that has multiple operating rooms sharing a single transportable IOEBT system. The invention also provides a mobile IOEBT system having an electron beam source mounted on movable mechanical supports. The IOEBT system is designed to be light enough to avoid the need to add structural support to preexisting medical care facilities. The IOEBT system of this invention requires only minimal additional radiation shielding.
The preferred embodiment of the electron beam therapy system of this invention includes a linear accelerator and microwave power source disposed in an accelerator head housing. The housing is mounted on a movable support that permits orientation of the electron beam applicator tube to the correct position with respect to the patient being treated.